Shadow of Night - All Souls Book 2 - Deborah Harkness

It began with A DISCOVERY OF WITCHES.

Historian Diana Bishop, descended from a line of powerful witches, and long-lived vampire Matthew Clairmont have broken the laws dividing creatures. When Diana discovered a significant alchemical manuscript in the Bodleian Library, she sparked a struggle in which she became bound to Matthew. Now the fragile coexistence of witches, daemons, vampires and humans is dangerously threatened.

Seeking safety, Diana and Matthew travel back in time to London, 1590. But they soon realise that the past may not provide a haven. Reclaiming his former identity as poet and spy for Queen Elizabeth, the vampire falls back in with a group of radicals known as the School of Night. Many are unruly daemons, the creative minds of the age, including playwright Christopher Marlowe and mathematician Thomas Harriot. Together Matthew and Diana scour Tudor London for the elusive manuscript Ashmole 782, and search for the witch who will teach Diana how to control her remarkable powers...